1. Field of the Invention
This invention relates to a controller of a flow quantity valve of a stepper motor type for controlling the flow quantity of a fluid flowing through a flow path disposed in an internal combustion engine and, for example, is applied to exhaust gas recirculation control valves, idle rotation speed control valves, etc.
2. Description of the Related Art
As an exhaust gas recirculation control valve used with an exhaust gas recirculation controller of an internal combustion engine, one which is opened and closed electrically by a stepper motor is already proposed, for example, as shown in Japanese Patent Unexamined Publication No. Hei 2-238162.
By the way, generally such an exhaust gas recirculation controller is not provided with a position sensor for detecting the valve position of an exhaust gas recirculation control valve for reducing costs. Thus, to know how much the exhaust gas recirculation control valve is opened, with a predetermined valve position as a reference point, the number of times a drive signal in the valve opening or closing direction has been given to a stepper motor is counted since the valve is at the reference point, thereby finding the assumed position of the valve, namely, the current opening of the exhaust gas recirculation control valve.
Therefore, with such an exhaust gas recirculation controller, it becomes important to move the valve position of the exhaust gas recirculation control valve to the reference point and reset the assumed position to a predetermined value at the reference point as initialization accurately.
Initialization in conventional exhaust gas recirculation controllers is, for example, to move a valve to the fully closed position and then reset the value of the assumed position to 0.
However, when the valve is fully closed, what phase the stepper motor is in is unknown, and the phase varies from one exhaust gas recirculation control valve to another.
For example, we will discuss this problem with an exhaust gas recirculation control valve using a four-phase stepper motor. When the valve is fully closed, the stepper motor also stops at a predetermined position. However, which of phases 0 to 3 the stepper motor at the predetermined position is in is unknown.
Therefore, to next drive the valve by one step in the valve opening direction, which phase 0 or 2 a drive signal for opening the valve by one step is to be given from is unknown; what drive signal is to be given to the stepper motor cannot be specified. If the stepper motor phase does not match the drive signal, the stepper motor cannot be turned.
Therefore, if the stepper motor phase does not match the drive signal, although a drive signal in the valve opening direction is given to the stepper motor five times, actually the valve may be driven by three steps. Thus, accurate exhaust gas recirculation control cannot be performed.
In the conventional exhaust gas recirculation controllers, initialization is executed only when the internal combustion engine is started or stopped. Thus, if the stepper motor moves out of adjustment during exhaust gas recirculation control, it cannot stay in adjustment until the key switch is handled.